Fiber optic connectors typically comprises a ferrule captivated by a coupling mechanism. The geometry of the coupling mechanism is generally independent of the ferrule. Ferrules may comprise a precision ferrule capillary providing a fiber retention and alignment function held by a ferrule base. Ferrule capillaries are known to be made of ceramic, metal and polymer. In the interest of minimizing fiber torsional stress, it is desirable that the ferrule capillary resist rotational displacement relative to the ferrule base at all times. During termination of a fiber optic connector, epoxy may be injected into a fiber passage internal to the ferrule. The process of injecting the epoxy subjects the ferrule capillary to an axial force, typically 5 lbs or less, relative to the ferrule base. It is desirable that the ferrule capillary resist axial movement in response to this "push out" force. As miniaturization is often an issue, it is desirable to have the axial and rotational antidisplacement features in a minimum amount of volumetric space.
A known ferrule capillary has a cylindrical volume with a notch at a nonmating end cut transverse to a longitudinal axis of the cylindrical volume. A ferrule base is overmolded at the notched end and surroundingly engages the notch. The notch resists axial and rotational displacement of the ferrule capillary relative to the ferrule base. The notch further provides for miniaturization by obviating the need to increase the diameter of the ferrule capillary in order to include antidisplacement features. With respect to metal or ceramic ferrules overmolded by a base, the notch may be machined into the ferrule in a secondary operation prior to overmolding.
With respect to polymer ferrules, the notch feature is undesirable because a mold that creates the notch has a relatively large single discontinuity therein. Fiber optic connectors and in particular the ferrules used therein are precision parts. The molding process, therefore, should be carefully controlled in order attain a manufacturing process having acceptable yields. Large discontinuities in a mold cavity tend to disturb the flow of the molten polymer as it enters the cavity during the molding process. This discontinuity makes it difficult to sufficiently control the molding process. It is desirable, therefore, for a polymer ferrule to be made in a mold wherein the number and size of discontinuities is minimized to streamline material flow.
An example of an overmolded ferrule is found in U.S. Pat. No. 5,375,183, the teachings of which are hereby incorporated by reference. A ferrule capillary comprises a cylindrical collar. The collar is overmolded by a base to form a fiber optic ferrule. The ferrule base should have a sufficient wall thickness to retain the ferrule capillary and to resist axial and rotational displacement thereto. In a competing concern, it is desirable to minimize the maximum outer diameter of a ferrule due to space limitations internal to various fiber optic connectors. It is desirable, therefore, to have a ferrule having a relatively small maximum outer diameter with sufficient retention of the ferrule capillary within the base.